The present invention relates to a liquid fuel burning device of wick evaporation type and, more particularly, to a liquid fuel burning device which is improved to prevent any reduction of fuel evaporation rate due to deposition of tar content to the fuel evaporation section of the wick and to smooth the transition from the ignition to a steady burning, while ensuring stable burning for a long period of time.
Hitherto, there have been proposed and used various types of so-called wick evaporation type liquid fuel burning device in which a liquid fuel sucked by the capillary action of a wick is evaporated and burnt at the end of the wick. Typical examples of such liquid fuel burning device is kerosene stoves, kerosene kitchen range and so forth.
These conventional liquid fuel burning devices, however, suffer various drawbacks. Namely, in the liquid fuel burning devices of wick evaporation type, it is extremely difficult to maintain a stable burning of liquid fuel. In addition, since the end of the wick where the liquid fuel is evaporated is subjected to a high temperature and sufficient oxygen during the burning, a part of the liquid fuel is easily changed into tar through oxidation, polymerization and condensation. The tar inconveniently deposits on the fuel evaporating portion of the wick to cause various troubles as stated below.
(1) The deposition of tar covers the surface of the fuel evaporating portion and clogs the internal capillary tubes to restrain the sucking action of fuel, as well as evaporation, resulting in a lowered rate of burning.
(2) The lowered rate of burning causes an unbalance between the air and fuel in the burning area to cause an imperfect burning to generate a large amount of carbon monoxide which is harmful to human bodies, while releasing offensive odor and much carbon.
(3) The deposition of tar increases the volume, i.e. the thickness, of the fuel evaporating portion of the wick. This dangerously interferes with the ability of the wick to be lowered for flame extinction.
(4) The tar inconveniently flows into the gap between the wick and the peripheral metallic sleeve supporting the wick, so as to allow the wick to stick to the sleeve to cause the same danger as mentioned in the above item (3).
(5) The accumulation of tar at the end of the fuel evaporating portion makes starting of the burning device difficult, and retards the propagation of flame after initiating a fire on the wick. Before the flame is propagated over the entire periphery of the wick, a large amount of carbon monoxide and carbon, as well as offensive odor, is released.
(6) The rate of supply of the air to the burner sleeve is determined by the draft, i.e. the wind generating force, of the burner sleeve, and is largely affected also by the ambient temperature and the presence of stream of a air or wind. The state of flame on the pores in the inner and outer flame sleeves in the burner sleeve is varied in accordance with the ratio between air and fuel, as well as the ambient temperature. Thus, the flames on the pores are easily formed and extinguished by an impact applied to the burner sleeve, presence of wind and so forth. In consequence, the evaporation latent heat supplied to the liquid fuel contained by the wick is easily changed. Thus, the burning is unstabilized by various external disturbance factors such as changes in the ambient temperature, wind, impact and the like.
The deposition of tar which causes the troubles mentioned in above items (1) to (5) is serious particularly when a part of the fuel has been degraded due to, for example, generation of oxides or peroxides as a result of application of heat or leaving the fuel for a long time in sun light, or when a different fraction of higher boiling point is mixed in the fuel as in the case of mixing of light oil, heavy oil, machine oil, salad oil or the like in the kerosene. In these cases, the deposition of tar takes place in a short period of time.